Residents dig out their cars as a snow plow clears the street in Queens, N.Y., on Jan. 3. / Daniel P. Derella, AP

by John Bacon, Mary Beth Marklein and William M. Welch, USA TODAY

by John Bacon, Mary Beth Marklein and William M. Welch, USA TODAY

A fresh blast of bitterly cold weather began sweeping across the nation Sunday, bringing snow, ice and frigid conditions to areas still digging out from earlier winter storms.

Much of the nation was bracing for what could be record low temperatures Monday and Tuesday.

"It's just a dangerous cold," National Weather Service meteorologist Butch Dye in Missouri said.

The massive attack of extreme cold, called a "polar vortex," was expected to bring low temperatures to more than half the nation Monday and Tuesday. Wind chill warnings stretched from Montana to Alabama.

The forecast is extreme: 25 below zero Fahrenheit in Chicago. Wind chills, what the temperature feels like with wind, could drop into the negative 50s and 60s in some places. Northeastern Montana was warned Sunday of wind chills up to 59 degrees below zero.

By Sunday evening, more than 4,000 flights had been canceled, creating more havoc for air travel. Another 10,000 more flights were delayed, according to FlightStats.com, and 1,446 flights into or out of Chicago's O'Hare airport were canceled.

"There is nothing routine about a weather event such as this," says Jim Hetzel, a vice president of FlightStats, based in Portland, Ore.

Several Midwestern states got up to a foot of new snow. More than 11 inches of snow fell in Chicago by Sunday evening - the most since Feb. 2, 2011, the weather service said. The St. Louis area had about a foot of snow, and southern Michigan could see up to 15 inches.

Indianapolis Mayor Greg Ballard upgraded the city's travel emergency level, making it illegal for anyone to drive except for emergency personnel, emergency purposes or seeking shelter. The last time the city issued a travel warning was during the 1978 blizzard.

Indianapolis International Airport spokesman Carlo Bertolini said crews were working to keep runways clear but the widespread cold and snow assured the disruptions would be severe. "You have cascading problems throughout the system," Bertolini said.

Stuck and weary travelers took to Twitter to vent about their frustrations

"Wrong time of year to be traveling :-)," wrote @davar.

"I am rotting in this airport. ... No crew?? Are you kidding me?" said @karlilj.

And "Dear @united, if the flight delays further, the next glass of wine is on you," @RanMan30 warned.

Not all travelers were complaining. At a Toronto airport, Danielle Inglis, who was heading to Sault Ste. Marie, Mich., for a women's curling competition, said people on her flight were friendly, sharing phone chargers and photos. "Since they're going to the north they kind of know what to expect,'' she said.

New York City and parts of the East were still wrestling with an earlier front that dumped a mix of snow, freezing rain and rain across much of the region.

At John F. Kennedy International Airport, a plane slid into snow Sunday morning, prompting the airport to suspend operations for about two hours because of icy runways.

There will be little rest for the weather-weary in the East. Kines said the bitter cold temperatures sweeping the Midwest will drive East Coast temperatures down through the day on Monday.

"Some place that could see temperatures near 50 early tomorrow could see single digits tomorrow night," Kines said.

In Orlando, Nan Connolly was enjoying shorts weather on Sunday, celebrating a break from "too-long summer" on the pool patio. But Kines warns that the latest cold front will push deep into the South. "A place like Orlando probably won't get out of the 40s on Tuesday," he said.

Those temperatures would be welcome relief to much of the Midwest, where temperatures dipped below zero in many areas. It was 15 degrees below in Watertown, S.D., early Sunday, Kines said. "You go up into parts of North Dakota and it was in the minus 20s. In some areas the wind chill is reaching minus 50. Just horrible."

The Midwest was bracing for a tough Monday.

Chicago called off school Monday, reversing an earlier decision to keep them open. Temperatures were expected to fall to minus 15 degrees there on Monday, with wind chills of 50 below zero possible.

Minnesota called off school Monday for the entire state - the first such closing in 17 years. Minneapolis was expecting a high temperature of minus 11.

But not everyone in the Upper Midwest is fretting too much about the latest winter front. In Albert Lea, Minn., John Rosenberg is using old-school remedies to help mitigate cold concerns. He has fueled up his car to combat moisture in the gas tank and has fans pointed at his windows so moisture doesn't build up and freeze on the glass.

"I'm manning the curtains in the house, making sure to capture the sunlight during the day and closing them promptly at night to retain as much short wave radiation as possible," he said.

In Bismarck, N.D., Chad Schmidt wasn't complaining about the temperature of minus 13 degrees, or even the wind chill of minus 46. "Being from North Dakota, we are used to it. ... A tough breed," he said. "Just bundle up to go out."